Method for activating and deactivating an image correction function, camera system and motor vehicle

Abstract

A method for operating a camera system of a motor vehicle, in which images of an environmental region of the motor vehicle are captured by means of an image sensor of the camera system via an optic device and an image correction function is activated by means of a control unit of the camera system, in which a light fall-off in a boundary region of the images caused by the optic device is compensated for, wherein a current brightness level of the environmental region is captured by means of the control unit and the activation and deactivation of the image correction function are effected depending on the current brightness level.

Claims

1. A method for operating a camera system of a motor vehicle, comprising: capturing images of an environmental region of the motor vehicle by means of an image sensor of the camera system via an optic device and an image correction function is activated by means of a control unit of the camera system, in which a light fall-off in a boundary region of the images caused by the optic device with a wide opening angle is compensated for, wherein a current brightness level of the environmental region is captured by means of the control unit and the activation and deactivation of the image correction function are effected depending on the current brightness level and depending on the current brightness level the camera system is switched from a normal light mode (NLM) to a low light mode (LLM), in which a gain factor and/or an exposure time are increased with respect to the normal light mode (NLM) and/or a frame rate (FR) of the image sensor is reduced, wherein the image correction function is deactivated upon switching to the low light mode (LLM) and is again activated upon switching again to the normal light mode (NLM); detecting a temperature of the image sensor; and effecting the switching based on a current value of the temperature by comparing a current value of an operating parameter of the image sensor, which is correlated with the brightness level and a gain factor, to at least one threshold, which is adjusted depending on the current value of the temperature.

2. The method according to claim 1, wherein an operating parameter of the image sensor is captured by means of the control unit, which is correlated with the brightness level of the environmental region, and the activation and deactivation of the image correction function are effected depending on a current value of the operating parameter.

3. The method according to claim 2, wherein a gain factor and/or an exposure time are used as operating parameter.

4. The method according to claim 1, wherein at a higher temperature, the at least one threshold is adjusted to a lower threshold value than at a lower temperature.

5. The method according to claim 1, wherein the image sensor is an HDR image sensor, by means of which HDR images of the environmental region are provided, wherein for providing an HDR image, at least two exposure time values of the HDR image sensor are adjusted, and wherein the image correction function is applied exclusively to pixels, which have been generated with a higher one of the exposure time values.

6. A camera system for a motor vehicle comprising: an optic device having a wide opening angle with an image sensor for providing images of an environmental region of the motor vehicle via the optic device; and a control unit for activating and deactivating an image correction function, in which a light fall-off in a boundary region of the images caused by the optic device is compensated for, wherein the control unit is adapted to capture a current brightness level of the environmental region and to activate and deactivate the image correction function depending on the current brightness level and depending on the current brightness level the camera system is switched from a normal light mode (NLM) to a low light mode (LLM), in which a gain factor and/or an exposure time are increased with respect to the normal light mode (NLM) and/or a frame rate (FR) of the image sensor is reduced, wherein the image correction function is deactivated upon switching to the low light mode (LLM) and is again activated upon switching again to the normal light mode (NLM), wherein a temperature of the image sensor is detected and the switching is effected based on a current value of the temperature, dependent on a comparison of the current value of an operating parameter of the image sensor, which is correlated with the brightness level and a gain factor, to at least one threshold, which is adjusted depending on the current value of the temperature.

7. A motor vehicle with a camera system according to claim 6.

Description

(1) There show:

(2) FIG. 1 in schematic illustration a motor vehicle with a camera system according to an embodiment of the invention;

(3) FIG. 2 in schematic illustration a block diagram of an individual camera of the camera system; and

(4) FIGS. 3 and 4 flow diagrams for explaining a method according to an embodiment of the invention.

(5) A motor vehicle 1 illustrated in FIG. 1 is for example a passenger car. The motor vehicle 1 includes a camera system 2, which has a plurality of cameras 3, 4, 5, 6 in the embodiment, which are disposed distributed on the motor vehicle 1. In the embodiment, four cameras 3, 4, 5, 6 are provided, wherein the invention is also not restricted to such a number and arrangement of the cameras 3, 4, 5, 6. Basically, any number of cameras can be used, which can be disposed at different locations of the motor vehicle 1. Alternatively to such a multi-camera system 2, a camera system 2 with a single camera can also be used.

(6) A first camera 3 is for example disposed on the front bumper of the motor vehicle. A second camera 4 is for example disposed in the rear region, for instance on the rear bumper or on a tailgate. The two lateral cameras 5, 6 can for example be integrated in the respective exterior mirrors. The cameras 3, 4, 5, 6 are electrically coupled to a central computing device 7, which in turn is coupled to a display device 8. The display device 8 can be an LCD display.

(7) The cameras 3, 4, 5, 6 are video cameras, which can each capture a sequence of images per time unit and communicate it to the computing device 7. The cameras 3, 4, 5, 6 each have a large opening angle, for instance in a range of values from 150° to 200°. They can also be so-called fish-eye cameras. Optionally, the cameras 3, 4, 5, 6 can also be HDR cameras.

(8) The camera 3 captures an environmental region 9 in front of the motor vehicle 1. The camera 4 captures an environmental region 10 behind the motor vehicle 1. The camera 5 captures a lateral environmental region 11 to the left of the motor vehicle 1, while the camera 6 captures an environmental region 12 on the right side of the motor vehicle. The cameras 3, 4, 5, 6 provide images of the respective environmental regions 9, 10, 11, 12 and communicate these images to the computing device 7. As is apparent from FIG. 1, the imaged environmental regions 9, 10, 11, 12 mutually overlap in pairs. From the images of the cameras 3, 4, 5, 6, the computing device 7 generates an image presentation, which is then displayed on the display device 8. This image presentation can for example be a plan view presentation, which shows the motor vehicle 1 and its environment 9, 10, 11, 12 from a bird's eye view.

(9) Therein, an exemplary construction of an individual camera 3 is shown in FIG. 2 in schematic and simplified manner. The camera 3 includes a communication interface 13, which is connected to a communication bus 14 of the motor vehicle 1. The camera 3 can communicate with the central computing device 7 via the communication bus 14.

(10) The camera 3 is a video camera. It includes an image sensor 15, which is disposed behind an optic device 16, in particular a lens. The image sensor 15 can for example be a CCD sensor or a CMOS sensor. The image sensor 15 is coupled to a control unit 17, which receives the digital images of the image sensor 15.

(11) The control unit 17 is also coupled to the interface 13, via which the control unit 17 communicates with the central computing device 7.

(12) As already explained, the camera 3 is illustrated in FIG. 2 in simplified manner. Therein, the image sensor 15 can also have an analog amplifier, by means of which the analog images are amplified with a gain factor G, besides the actual image array, by means of which the analog images are generated. In addition, the image sensor 15 can also include an AD converter, by means of which the analog images are converted to digital images.

(13) Various operating parameters of the image sensor 15 can be adjusted by means of the control unit 17. Among other things, the mentioned gain factor G, a frame rate FR as well as an exposure time E are adjusted by means of the control unit 17. Alternatively, these operating parameters G, FR, E can also be preset by the central computing device 7.

(14) The camera 3 also includes a temperature sensor 18 capturing the current temperature T of the image sensor 15 and communicating it to the control unit 17. Alternatively, the temperature T can also be computationally determined based on the image data.

(15) The camera 3 can be switched between a normal light mode NLM and a low light mode LLM. The switching of the camera 3 is now explained in more detail with reference to FIG. 3. The method starts in a step S1 and proceeds to a step S2, in which the normal light mode NLM is activated. Here, the frame rate FR is adjusted to a first value, for example 30 images per second. In this normal light mode, the gain factor G and the exposure time E are also lower than in the low light mode LLM.

(16) The control unit 17 then continuously checks in real-time if the current gain factor G exceeds a first threshold TG1. If G is greater than TG1, the method proceeds to a step S3, in which the camera 3 is switched to the low light mode LLM. In this low light mode LLM, the frame rate FR is reduced to a second value, which may for example be 15 images per second. If the camera 3 is in the low light mode, thus, the control unit 17 checks if the gain factor G falls below a second threshold TG2. This second threshold TG2 is smaller than the first threshold TG1. Alternatively, a same threshold can also be used. By providing two different thresholds TG1 and TG2, a hysteresis is implemented such that the switching is overall effected more robustly. Thus, frequent switching operations are prevented.

(17) The two thresholds TG1 and TG2 can also be adjusted depending on the current temperature T. A method for adjusting the thresholds TG1 and TG2 is explained in more detail with reference to FIG. 4:

(18) This method starts in a step S10 and proceeds to a step S11, in which the first threshold TG1 is set to a first threshold value TG11. At the same time, the second threshold TG2 is set to a second value TG21, wherein TG21<TG11.

(19) If the temperature T now exceeds a first temperature threshold value TT1, thus, the method proceeds to a further step S12, in which the two thresholds TG1 and TG2 are reduced and herein are set to a third value TG12 and a fourth value TG22, respectively, wherein TG12<TG11 and TG22<TG21. Preferably, the following relation can also apply: (TG12−TG22)=(TG11−TG21). In other words, the difference between the first threshold TG1 and the second threshold TG2 can remain constant.

(20) If the temperature T now deceeds again a second temperature threshold value TT2, thus, the method again returns to the step S11 such that the thresholds TG1 and TG2 are again increased. Therein, the second temperature threshold value TT2 is smaller than the first temperature threshold value TT1. Thereby too, a hysteresis is provided such that frequent switching between the thresholds is prevented. However, alternatively, a single temperature threshold value can also be used. Then, it applies: TT1=TT2.

(21) In the embodiment, the following values can be used: TT1=70° C. and TT2=65° C. Generally, a difference between the temperature threshold values TT1 and TT2 can be in a range of values from 0 to 10° C.

(22) In the control unit 17 (or alternatively in the computing device 7), an image correction function is also implemented, which serves for compensation for a light fall-off in the boundary region of the images, which is caused by the optic device 16 and more precisely by the wide opening angle larger than 160°. This image correction function provides that the brightness values—namely the Y values—of the pixels in the boundary region of the images are multiplied by a compensation factor and thus amplified. This compensation factor can also be different for different pixels, namely depending on the distance to the boundary of the image. The compensation factor can in particular be greater towards the image boundary.

(23) This image correction function is now activated exclusively in the normal light mode NLM and deactivated upon switching to the low light mode LLM. If the camera 3 is again switched to the normal light mode NLM, thus, the image correction function is again activated. The activation and deactivation of the image correction function are therefore depending on the current brightness of the environment 9, 10, 11, 12 of the motor vehicle 1.

(24) Alternatively to a non-HDR image sensor 15, an HDR image sensor 15 can also be employed, by means of which HDR images of the environment 9, 10, 11, 12 are provided. For providing an HDR image, therein, two conventional images are captured with different exposure times E and processed together to an HDR image. Here, the image correction function can be applied exclusively to that image or those pixels, which have been generated with the higher exposure time.